Variable voltage transformer



Dec. 9, 1941. H, L. MEKELBURG ETAL 2,265,666

VARIABLE VOLTAGE TRANSFORMER Filed March 13, 1939 2 Sheets-Sheet l 1941-H. L. MEKELBURG ETAL 2,255,666

VARIABLE VOLTAGE TRANSFORMER Filed uarch'ls, 1939 2 Sheets-Sheet 2 5%5mm i; MA

Patented Dec. 9, 1941 VARIABLE VOLTAGE TRANSFORMER Harold L. Mekelburg,Milwaukee, and Carroll Stansbury, Wauwatosa, Wia, assignors toCutler-Hammer, Inc., Milwaukee, Wis., a corporation of DelawareApplication March 13, 1939, Serial No. 261,458

8 Claims.

This invention relates to variable voltage transformers and while notlimited thereto is particularly applicable to variable voltageautotransformer dimmers for illumination control systems.

An object of the invention is to provide an improved transformer of theaforementioned type which is compact and has a large capacity for itssize.

Another object is to provide a transformer which occupies a minimum ofmounting space.

Another object is to provide a transformer which can be readily mountedin different positions to meet various space and operating conditions.

Another object is to provide a transformer which can be readily mountedin groups to be operated at will jointly or separately.

Another object is to provide a regulating transformer which has highheat radiating capacity.

Another object is to provide a transformer in which the heat radiatingsurfaces of the transformer itself are amplified by that of the otherparts thereof.

Other objects and advantages will hereinafter appear.

The accompanying drawings are illustrative of an embodiment of theinvention. In the drawings:

Figure 1 is a side view of a transformer.

Fig. 2 is a front view of the control part of the transformer shown inFig. l with certain parts removed.

Fig. 3 is a top view of the contact mechanism.

Fig. 4 is a section of the device along the line 4-4 in Fig. 1.

Fig. 5 is a top view of certain details of the brush holders.

Fig. 6 is a rear view of the device.

Fig. 'l is a wiring diagram thereof.

The transformer comprises a ring shaped core I made of closely woundcoil of strip steel. A magnetizing coil 2 of insulated wire is wound onsaid core in such a manner that the wires thereof are closely spaced toform a single layer on the outer perimeter of the core. The uppersurface 3 of the wires on the outer cylindrical surface of the core isbared of insulation and the space between the wires is filled with asolid insulating material. After assembly with its support the entireouter cylindrical surface is finished to form a smooth commutator-likesurface. The winding of the coil covers about 340 degrees of the entirecircumference of the core, the ends of the winding being attached toterminals as will be ex plained hereinafter.

The core with the winding placed thereon as aforedescribed is fastenedto a hub or support 4 by means of an electrical insulating cement I ofgood heat conductivity so as to form with the hub a solid self-containedstructure. The cement employed may be a thermoplastic substance, ahydraulic cement or any other substance which is easily applied andwhich subsequently holds the parts rigidly together and assures goodheat conductivity therebetween. This construction assures great rigidityand accurate centering of the cylindrical contact surface of the windingwith respect to the hub center. It further assures rapid transmission'ofheat from the winding to the hub thereby substantially increasing theeffective heat radiating surface of the transformer.

The hub 4 is provided with a central huh I forming with rollers I aneedle bearing for a shaft 8. One end of the shaft which protrudesoutside of the bearing is provided with a section of reduced diameter 9which is adapted to receive the hub ill of a contact lever II, the hubbeing fastened to the shaft by a press fit and the frictional engagementbetween the parts may be increased by roughening of the shaft.

An insulating plate I2 is fastened to the hub Ill by means of rivets orbolts l3 and to the plate in turn is riveted the diametrically extendingarm l4 of the contact lever H which is thus rigidly connected to butinsulated from the hub. The rivets or bolts l3 project axially throughthe hub, one on each side of the arm H, for a purpose to be explainedhereinafter. A substantially radial lug I! cast integrally with the hubI0 is adapted to engage a stop to limit the rotation of the contact arm.The stop comprises a bolt l8 slidably mounted in the support 4 andbiased outwardly by a spring H. The bolt near its outer end is conicaland upon engagement with a suitably shaped surface of the lug Illspushed inwardly, thereby compressing the spring I! and graduallyincreasing the resistance of the lever H to further rotation, until itcomes to a stop by engagement of the lug with a reduced cylindricalextension of the conical portion of the bolt. The outward movement ofthe bolt II is limited by a pin through the rearward end of the bolt,which pin engages an abutment of the hub 4.

The hub 4 is bolted to a bracket I! which is a substantially flat metalplate arranged at right angles to the central axis of the transformerand at one side of the latter. By being in intimate heat transmittingcontact over its entire peripheral edge with the plate the radiatingsurface of the hub is further amplified. The plate |9 has its oppositeends and 2| and one side 22 upturned to provide feet for mounting thesame inside of a frame 23 which surrounds the transformer at itsperimeter and at some distance therefrom. V

A pinion 24 is rigidly mounted on the shaft 8 at the end opposite tothat on which the hub. I0 is mounted. The pinion is provided at one sidethereof with two axial clutch jaws 25, the purpose of which will beexplained in detail -hereinafter. A gear sector 26 which engages thepinion 24 is rotatably mounted on a stud 21 which in turn is mounted onthe bracket IS. The sector 26 is provided with a clevis 28 to whichmaybe attached a reciprocable operating rod 23 by means of which thetransformer lever is rotated. I

The arm I4 carries at one end a pin 30 on which are pivotally mountedthe ends of a number of substantially semi-circular brackets 3|, eachcomprising two parallel spaced fiat strips fastened together atintervals by means of rivets with spacers 32 interposed between thestrips to maintain their spacing. The opposite ends of said brackets"form closed forks in which are slidingly fitted headed bolts 33. Aspring 34 is interposed between the head at the inner end of the-boltandthe fork so as to urge said bolt inwardly of the fork, The outer ends ofthe bolts passthrough properly spaced holes in the end- 35 of the arm l4opposite 'the end which carries the ,pi'n30. For this purpose the arm isbent at substantially right angles to its main portion, so asto beparallelito the in :0. Individual cotter pins 36 inside of the lever end35 and a single pin 31 common to all bolts outside of the lever end 35'retain said bolts in engagement with the arm. A contact brush 38,preferably of carbon is mounted in'a brush holder 39 on each bracket 3|intermediate of its ends in such a manner as to make contact with thebared wires 3 of the transformer as the contact lever is rotated. Bythismeans each individual brush make contact with. the wires of thetransformer winding. A fiat retainer 4| has a recess which fits over thebrush. The brush and the retainer are assembled between the two stripswhich form' the brackets 3| and pressure is applied to thebrush byscrews 42 on either side of the brush, which screws also serve toconfine the retainer. If one of the-brush extensions has been worn downdue to extensive use the brush may be reversed so as to use the otherextension thereof. The arms", being in good heat conducting contact withthe brushes, serve to in crease the effective heat radiating surface ofthe latter to keep them cool and prevent overheating of the winding atthe points of contact.

To conduct the current from the lever H to the outside circuit,,theformer is provided with a circular slip ring 43, conductively fastenedto the lever. A spring-pressed brush 44 is mounted on an insulatingblock 45 so as to engage the slip ring 43 asthe latter rotates. Theblock 45 fedly attached tothe core I and serving to anchor the ends ofthe winding 2 and to conduct the current to the latter.

A limit switch is interposed between the terminal 5| and the terminal 52for opening one side of the power supply circuit after the voltage ofthe lamp circuit has been reduced to the minimum value. The line wires1.. and L are confiected to the terminals and 52, respectively,

while the lamp circuit is connected between the terminals 48 and 50. Thelimit switch comprises a lever 51 which normally bridges contacts 53 and59, respectively, connected to the terminals 5| and 52. The lever isbiased to circuit closing position bya spring cooperating with a bolt 6|which is fastened to the insulating block 43.

The lever 51 is provided with an extension 62 which is adapted to abutan insulating block 63 attached to one end of the lever II when thelatter is in the position corresponding to minimum lamp voltage. In thisPosition the block 63 lifts the lever 51 out of contact with one or bothof the contacts 58 and 59, thereby opening the circuit asaforedescribed;

If it is desired to couple two transformers together and operate them bya single operating rod they are mounted as shown in Fig. 4 at a suitablelateral distance'from each other on a supporting frame 84 and aninsulating disc or coupling 65 having recesses to receive the pins l3and the jaws 25, respectively, is interposed so as to engage said pinsand laws, thereby providing a driving connection between the shafts 3 ofadjacent transformers and permitting power transmission from one to theother.

What we claim as new and desire to secure by Letters Patent is:

1. An alternating current transformer comprising, a circular iron core,an inducing winding on said core having its turns arranged to form acommutator on a surface of said winding, a brush adapted to complete acircuit including a variable section of said winding through saidcommutator, and means to dissipate heat to the ambient air, including ahub to support said core and said brush, and further including a fillingof electrical insulating cement or good heat conductivity interposedbetween said winding and said hub for attaching the former to the latterand to facilitate the conduction of .heat from said core to said hub tothereby increase the heat dissipating capacity of said transformer, saidcement forming the sole supporting connection between said hub and thecore with'its inducing winding.

2. An alternating current transformer comprising, a circular iron core,an inducing winding'on said core having its tums arranged to form acommutator on a surface of said winding, a contact brush for saidcommutator including means to oscillate said brush about the center ofsaid core, and means to dissipate heat to the ambient air, including ahub to support said core and said oscillating means. and including afilling of electrical insulating cement of good heat conductivityinterposed between said winding and aacaeee said hub for attaching theformer to the latter and to facilitate the conduction of heat from saidcore to said hub to thereby increase the heat dissipating capacityof'said transformer, said cement forming the sole supporting connectionbetween said hub and the core with its inducing winding.

3. An alternating current transformer comprising,.a circular iron core,an inducing winding on said core having its turns arranged to form acommutator on a surface of said winding, and a heat dissipating supportfor said core and its winding including a metal hub concentric with andprojecting inside of said core and its winding and attached theretosolely by an interposed filling of electrical insulating cement of goodheat conducting capacity, said cement completely filling the spacebetween said hub and the inside perimeter of said core and its winding,to thereby amplify the heat radiating capacity of said core.

4. An alternating current transformer comprising, a circular ironcore,'an inducing winding on said core havingits turns arranged to forma commutator on a surface of said winding, a contact brush cooperatingwith said commutator and oscillatable around the central axis of saidcore, a heat dissipating support for said core and its winding includinga metal hub concentric with and projecting inside of said core and itswinding and having a pivot for said brush, and a solidifled electricalinsulating cement of good heat conductivity filling the space betweensaid hub and the inside perimeter of said core and its winding andforming the sole means to assemble them into a unitary structure and toamplify the heat radiating capacity of said core.

5. A contact for cooperating with and movable relative to and concentricwith a cylindrical commutator comprising, a rotating shaft, a doubleended lever attached intermediate its ends to said shaft, asubstantially semi-circular arm of high heat conductivity having its oneend pivoted at one end of said lever for rotation in a planeperpendicular to said shaft and having its other end resilientlyattached to the other end of said lever to bias it toward said shaft,and a contact brush attached to said arm in heat conducting relationthereto, whereby said arm amplifies the heat radiating capacity of saidbrush.

6. A contact brush for cooperating with a cylindrical commutator and arotatable concentric with the latter comprising, a rotating shaftsupported concentric with a cylindrical commutator, means to rotate saidshaft, a double ended lever attached intermediate its ends to saidshaft, a substantially semi-circular arm of high heat conductivityhaving its one end pivoted at one end of said lever for rotation in aplane perpendicular to said shaft and having its other end resilientlyattached to the other end of said lever to bias it toward said shaft,and a contact brush attached to said arm in heat conducting relation,whereby said am amplifies the heat radiating capacity of said brush,

7. A contact mechanism for completing a circuit between varying pointsof a stationary cylindrical commutator and a stationary terminalcomprising, a support arranged for mounting in fixed relation to acylindrical commutator, a rotatable shaft journaled on said support forrotation concentric with said commutator, a double ended leverinsulatedly attached intermediate its ends to said shaft, asubstantially semi-circular arm having its one end pivoted at one end ofsaid lever for rotation in a plane perpendicular to said shaft andhaving its other end resiliently attached to the other end of said leverto bias it toward said shaft, a contact brush at-' tached to said arm, aslip ring attached to said arm concentric with said shaft, a secondcontact brush insulatedly mounted on said support and arranged tocontact said ring and provided with a terminal.

8. An alternating current transformer comprising a circular iron core,an inducing winding on said core having its turns arranged to form acommuator on a surface of said winding, a support for said coreincluding a hub concentric with and projecting inside of said core andhaving 'therein an opening providing a pivot bearing, a

solidified heat conducting cement interposed between said core and saidhub to assembly them into a unitary structure and to amplify the heatradiating capacity of said core, a contact brush cooperativelyengagingsaid commutator and rotatably movable with respect thereto, mountingmeans for said contact brush comprising a rotatable shaft adapted forsupport within said pivot bearing, a double-ended lever attached in--termediate its ends to said shaft, and a substantially semicircular armof high heat conductivity having one end thereof pivotally connected toone end of said lever for rotation in a plane perpendicular to saidshaft and having its other end yieldably attached to the other end ofsaid lever to bias said arm toward said shaft, said contact brush beingattached to said arm in heat conducting relation thereto, whereby saidarm amplifies the heat radiating capacity ofsaid contact brush.

, HAROLD L. MEKELBURG. CARROLL STANSBURY.

